The present invention relates to a device for controlling an internal combustion engine fuel injector.
Known injectors normally comprise a nozzle control rod controlled hydraulically by a metering valve, which comprises a valve body having a rod guide seat coaxial with a control chamber supplied with pressurized fuel. The control chamber communicates with a discharge chamber via a discharge conduit normally closed by a shutter controlled by an electromagnet.
To close the control chamber temporarily when the metering valve is opened, the control rod normally comprises a portion which is arrested against a flat end surface of the guide seat in the valve body; and, to reduce fuel flow when the metering valve is open, the lateral surface of the control rod, positioned closing the control chamber, normally partially closes the pressurized fuel inlet conduit adjacent to the flat surface of the rod guide seat.
A major drawback of known injectors of the above type is the considerable axial rebound of the rod on impact with the flat surface of the valve body, so that fuel flows into the control chamber, thus resulting in forced oscillation of the rod about the hydraulic balance position, and in irregular fuel supply by the injector, which calls for fluctuating opening and closing times of the nozzle by the central control unit.
To reduce such oscillation, injectors have been proposed in which the surface arresting the rod is provided with micrometric grooves to prevent closing the control chamber entirely as the metering valve is opened, so that a certain amount of fuel continues to flow inside the control chamber to damp oscillation of the rod. Such flow, however, impairs the injector nozzle opening response of the rod, while at the same time circulating fuel to no purpose. Moreover, formation of the micrometric grooves is fairly expensive.